Various studies have conventionally been carried out for the purpose of improving the toughness, the wear resistance and the corrosion resistance of a titanium carbide base cermet, and recently an improved titanium carbide base cermet was developed, which contains added titanium nitride (TiN) or titanium carbo-nitride (TiCN). More specifically, TiN is one of the most stable nitrides, together with zirconium nitride (ZrN) among transition metal nitrides, excellent in the strength at high temperatures, has such a high hardness as a Vickers hardness of 1,950 kg/mm.sup.2, and is far superior to titanium carbide (TiC) in terms of the corrosion resistance. TiCN has also excellent properties similar to those of TiN. It is therefore considered that by adding TiN or TiCN having such excellent properties to a titanium carbide base cermet, the grain growth in the dispersed phase is largely inhibited at the time of sintering said cermet, and hence, improves the toughness of the titanium carbide base cermet.
The following cermet has been proposed:
a titanium carbide base cermet, disclosed in Japanese Patent Provisional Publication No. 65,117/77 of May 30, 1977 (Japanese Patent Application No. 140,277/76 of Nov. 24, 1976) corresponding to the U.S. patent application Ser. No. 634,972 of Nov. 24, 1975, which consists essentially of:
a dispersed phase of from 50 to 90 wt.% consisting essentially of titanium carbide and vanadium carbide as indispensable constituents, and at least one of chromium carbide, molybdenum carbide and titanium nitride; and
a binder phase of from 10 to 50 wt % consisting essentially of nickel, molybdenum and aluminum (hereinafter referred to as "Reference 1").
Titanium nitride (TiN) is contained in Reference 1 as an optional constituent in the dispersed phase thereof. TiN has the function of improving the hardness and the toughness of a titanium carbide base cermet, as mentioned above, as well as of improving the wear resistance, especially the resistance to crater wear. On the other hand, however, if TiN is contained in the dispersed phase, it is inevitable that the wettability of the dispersed phase against the binder phase tends to be adversely affected. Addition of TiN alone cannot therefore always improve the toughness of a titanium carbide cermet as desired.
In Reference 1 the dispersed phase contains chromium carbide (Cr.sub.3 C.sub.2) as an optional constituent. Cr.sub.3 C.sub.2 has the function of improving the hardness of the dispersed phase as well as of improving the strength and the corrosion resistance of the binder phase by chromium produced through partial decomposition of Cr.sub.3 C.sub.2, which dissolves into the binder phase to form a solid-solution therewith. Addition of Cr.sub.3 Cr.sub.2 to the dispersed phase therefore improves the hardness, the heat resistance and the corrosion resistance of a titanium carbide base cermet, while deteriorating the toughness thereof.
In Reference 1 also, the binder phase contains aluminum (Al) as an indispensable constituent, Al dissolves into the binder phase to form a solid-solution therewith, and when the binder phase mainly comprises nickel, a .gamma.'phase [Ni.sub.3 Al(Ti)] with fine grains is precipitated in the binder phase, thus strengthening the binder phase, as mentioned later. The aforementioned effect of Al addition is however limited to the strengthening of only the binder phase, and does not strengthen the dispersed phase.
With these facts in view, the conventional titanium carbide base cermet containing TiN has improved toughness, wear resistance and corrosion resistance as compared with those of a titanium carbide base cermet not containing TiN, under the effect of TiN addition. However, the conventional titanium carbide base cermet cannot be said to be provided with the creep resistance, the wear resistance and the impact resistance at high temperatures sufficient to serve as a material for a high-speed cutting tool which produces much heat, a hot forging die and a hot rolling roll.